Effect of Hay Substitution on Intake and Digestibility of Forage Rape (Brassica napus) Fed to Lambs2

Abstract

Intake and digestibility trials were conducted with sheep to evaluate the effect of adding various levels of a typical fibrous grass forage (neutral detergent fiber, NDF = 68%) to a high quality, low fiber (NDF = 22%) brassica forage. Four forage rape:orchardgrass hay diets (0, 40, 70, 100% rape content on a dry matter basis) were fed to groups of six Polled-Dorset crossbred growing wether lambs (39.6 kg) individually housed in metabolism crates. After a 7-d ad libitum intake period, a 7-d digestibility trial was conducted at 90% of the observed ad libitum intake level. Digestible dry matter intake (DDMI) per unit metabolic body weight increased as rape in the diet was increased from 0 to 70%, with increases in both dry matter intake and dry matter digestibility (DMD). However, DDMI was similar for lambs fed the 70 and 100% rape diets, with DMI decreasing to the same relative extent as DMD increased. Digestibility of the cell wall fraction of the two intermediate diets (40% rape and 70% rape) was lower than predicted from component forage digestibilities. This observation suggests the existence of an associative effect similar to that often reported when forage and concentrates are fed in various ratios. Forage brassicas appear to be utilized in the ruminant in a manner more typically resembling a concentrate than a forage.

A note on the effect of dietary proportions of kale (Brassica oleracea) and grass silage on rumen pH and volatile fatty acid concentrations in dry dairy cows

“…Lambert et al (1987) observed that lambs offered 100% rape relative to a 70% rape diet had reduced DMI by 15%, suggesting that the low DM concentration of brassica (i.e. kale, rape) forages reduced DMI via the gut fill effect of intracellular water.…”

“…However, the greater buffering properties of kale compared to grass silage probably contributed to the absence of a depression in ruminal pH as dietary grass silage proportion decreased. Brassicas contain about 80-95% water (Lambert et al, 1987); the high bulk density of forage kale has been shown to increase mastication in cows (Gazzola et al, 2007) thus increasing saliva production and consequently buffering rumen pH which probably contributed to the absence of a larger decline in rumen pH on diet K100.…”

“…While numerous studies have examined the effects of brassica forages on sheep metabolism and performance (Vipond et al, 1998;Cassida et al, 1994;Lambert et al, 1987) there is a scarcity of published literature reporting the effects of brassica forages on rumen physiology in the dairy cow. Kale contains high concentrations of readily fermentable carbohydrate (CHO) (water soluble CHO and pectin), and low concentrations of structural CHO (hemicellulose and cellulose) (Barry and Manley, 1985).…”

The effect of sowing date and nitrogen on the dry‐matter yield and nitrogen content of forage rape (Brassica napus L.) and stubble turnips (Brassica rapa L.) in Ireland

“…However, the ability of forage rape and stubble turnips, irrespective of nitrogen level and sowing date, to maintain CP concentrations over the growing season allows considerable flexibility to the producer when utilizing the forage crops with animals. Furthermore, in vitro digestibilities are consistently high among forage brassica crops and may exceed 900 g kg −1 (Lambert et al. , 1987; Armstrong et al.…”

Productivity and Health of Gestating Ewes Grazing Tyfon Pastures Containing Weeds

“…The high water content of brassica forage may physically limit feed consumption (Lambert et al, 1987;GuiUard et al, 1988). Low-fiber brassica forage is similar in composition to a high-moisture concentrate feed (Guillard and Allinson, 1988) and may be unsuitable as the sole diet for ruminants (Lambert et al, 1987;Cassida, 1992). Provision of hay to animals grazing brassica pastures addresses these concerns by diluting antiquality compounds and increasing dry matter (DM) and fiber content of diets.…”